The present invention relates to a projection type image display apparatus for displaying images by using laser as a light source.
As an image display apparatus capable of large-screen display, there is known a projection type image display apparatus, i.e., so-called projector apparatus.
In the projection type image display apparatus, it is considered to display images by scanning with a laser beam using a laser light as a light source, in view of its merits such as easiness of modulation by a picture signal, good color reproduction performance, and capability of sufficiently securing brightness (see, for example, Japanese Patent Laid-open No. Hei 3-65916).
Meanwhile, since the laser light is emitted from a very small light emitting point and is a parallel light with a small divergence angle, viewing into the light causes the light to be condensed as a small point on the retina of the eye, and, when the laser power is high, the retina of the eye undergoes a burn.
Therefore, as to laser light using apparatuses, the international laser safety standards IEC60825 series and the related domestic standards of individual countries provide severe safety standards for the producers and users of laser apparatuses. For example, IEC60825-1 provides class classifications from Class 1 to Class 4 according to the magnitude of laser power, and, for each of the classes, provides a guide to be observed by the producers and users.
In recent years, for example, laser light shows using sharp-colored laser beams have come to be performed in large events and the like.
In the cases of the laser light shows, also, the producers and users of the laser apparatuses must deal with the laser light on the basis of the above-mentioned safety standards. For example, in order to perform a laser light show with brighter laser beams, a manager skilled in the art of laser apparatuses must be present.
On the other hand, in the cases of image display apparatuses in which a screen is scanned with laser beams, the laser light diffused and reflected upon once impinging on the screen is diffused in all directions, so that it is confirmed that even a laser with considerable intensity (laser class classification 3B or below) is safe.
However, if one should erroneously and directly look at the laser beam before irradiation of a screen therewith, there is the possibility that the retina of the eye might undergo a burn when the light quantity of the laser beam is large.
As a method for solving the above problem, the following methods may be contemplated.
A first method is a method in which the laser beam is operated in such a range that even the direct incidence of the laser beam on the eye is safe. Specifically, though differing according to laser beam exposure conditions, the laser beam is operated in the range of Laser Class 1 or 2.
A second method is a method in which a shield is provided so that people cannot enter a laser irradiation space, thereby making it impossible for the audience from directly peeping into the laser beam.
A third method is a method in which intrusion of a person into the laser irradiation space is supervised, so as to make it impossible for the audience from directly peeping into the laser beam, and, if there is some intruding object into the irradiation space, the output of the laser light is lowered to such an extent as to be non-harmful to human beings.
In the first method, however, the laser power is restricted to a low level, so that it is impossible to display images brightly. Therefore, it is impossible to sufficiently display the merits of the use of laser beams.
Besides, in the second method, it is highly possible that the shield may obstruct the view of the audience.
In view of the above, the third method is considered to be the most desirable, with minimum influence on the quality of the images displayed.
As a configuration realizing the third method, there is considered a configuration which includes an image display region space scanned with a laser beam for image display and in which the space including a certain extent of peripheral region space is supervised, and, in consideration of the intruding speed of a person, the output of the laser beam is lowered to such a degree as not to be harmful to the person, before the person reaches to the image display region.
Where this configuration is adopted, however, there are the following demerits.
Firstly, even where the person stays only in the peripheral region space and he does not enter the image display region space scanned with the laser beam, the luminance of image display would be lowered.
Secondly, in a configuration in which the supervision is conducted by use of only one sensor, the luminance of the image display as a whole is lowered, in whatever region of a part of the supervised region the abnormality is sensed (the intruding object is sensed).
For example, when the current international laser safety standard (IEC60825-1) is interpreted on the most safe side, a finger of a child must be detected, and the luminance of the image display as a whole would be lowered even where an insect comparable to the child's finger in size (diameter: about 12 mm) has flown and intruded.
In view of this, it may be considered to adopt a configuration in which the supervision is conducted by a plurality of sensors, or a configuration in which a high level of image processing is conducted to determine the intrusion position of the intruding object, and the luminance of image display is lowered only at the part near the intrusion position. Where such a configuration is adopted, the equipment cost is increased accordingly.
Thirdly, the broad region including the range from the projection lens to the image display screen which is a two-dimensional plain surface must always be monitored, so that it takes a longer time until a detection signal is outputted, as compared with the case where the monitoring is conducted one-dimensionally or at a point or points.